Complex electronic equipment often includes a rack that holds many replaceable circuit modules. Each circuit module may contain one or more circuit boards with multiple integrated circuits and other interconnected components, and one or more connectors with multiple contacts at its rear end. A technician places the module on a track of the rack, and slides the module rearwardly until the contacts on the module lie close to corresponding contacts on the rack-mounted connector. An insertion-retention device is then operated to advance the module to its final position, to overcome the resistance of multiple mating contacts and the friction of guide surfaces such as formed by the interfitting connector housings. Only the front of the module is accessible for operating the device, and if the device pushes against the front of the module then the module must be made rigid, which adds to the cost. If the housings of the connectors on the module are relied upon for controlling the positions of the contacts to assure they mate with contacts of the rack-mounted connectors, then the contacts and other mating parts must be closely positioned with respect to the connector housing, which can be difficult. Furthermore, if the module contains two or more connectors, care must be taken to assure that the aligning surfaces for both connectors are accurately positioned with respect to each other. This is difficult, especially because minimum clearances are required on interfitting connector shells. In a vibration environment these clearances allow rapid sliding or "fretting" of the contacts which leads to premature failure. It is desirable that the insertion-retention device advance the top and bottom of the module in unison to avoid cocking of the module, and yet only a limited force should be applied to avoid damage if there is an obstruction. A circuit system which avoided the above disadvantage of prior systems, would be of considerable value.